JOURNAL OF FACULTY OF ENGINEERING (UNIVERSITY OF TABRIZ)
Year:2007 | Volume:34 | Issue:1 (46) ELECTRICAL ENGINEERING|Papers Count:10

The recent advances in high-power semiconductor technology have made control of electric power in transmission lines more reliable and faster. Nowadays, FACTS devices are used in power systems in controlling and compensation of transmission lines. These devices are based on semiconductor and electronic technology that have advantages over traditional controlling devices. UPFC is one of the most recent kinds of FACTS that are made up from two PWM converters, which share a single dc link. UPFC is a controlling device in power systems that can control three important parameters, namely, impedance, voltage and phase angle, simultaneously. In addition, it is widely used in harmonic compensation in power systems. In this paper, based on instantaneous power theory, a control strategy has been developed to improve UPFC operation for simultaneous harmonic compensation and power flow control. The two main features of the proposed control model are improvement of dynamic stability and reduction of interaction between real and reactive powers. The simulation results clearly show satisfactory performance of the proposed model.

In this paper a novel method for the solution of parabolic equations is presented. The solution of parabolic equation is expanded by the 2nd order spline basis function. Then the expansion coefficients are computed by the least square method (LSM). The minimization of least square functional directly leads to the solution of the parabolic equation. It will be seen that the proposed LSM is more reliable than the split step method, because it can be applied over impedance boundaries in a simple manner. In comparison with the finite difference method, the proposed LSM is very fast.

Data requirements and large computation times are still major difficulties in reliability evaluation of large-scale composite systems. Equivalent methods are normally used to assess reliability in these systems. A novel equivalent approach based on graph theory is presented in this paper for reliability assessment of a small area in a large-scale power system. In this approach, the entire power system is divided into two parts of area of interest and interconnected area. Two new indices are first defined for the generation and load points associated with the interconnected area. Then using these indices, interconnected area buses are simplified and a new graph network is made. The effects of interconnected area on the area of interest are modeled with a graph network. The applicability of the proposed approach is examined using the IEEE-RTS network and the results are presented and compared for various case studies

The aim of this work is to investigate and evaluate the performance of Unified Power Flow Controller (UPFC) devices operating in a transmission system, in order to control interarea oscillations originated by small disturbances. Studies have been carried out on a linearised modified Heffron-Phillips model of a power system installed with a UPFC. Investigations have been done to understand relative effectiveness of modulation of the UPFC control signals, Le. modulation index of shunt converter (mE), phase angle of shunt converter voltage(dn), modulation index of series converter (mn), phase angle of series converter voltage(dE) and their variations on damping of system oscillations using controllability index. Investigations reveal that alternative damping controllers (damping controller mB and dE and dual damping controller) provide robust performance under wide variations in loading conditions and system parameters.

The dynamic voltage restorer (DVR) is the most advanced mitigation device that has been proposed to protect sensitive loads from the effects of voltage sags. The performance of DVR depends on the ability of PWM scheme to produce the required voltage and the control method. To improve transient and steady state response of DVR, in this paper a new closed 100p control based on the state feedback is proposed. Since the inverter switching using space vector modulation gives some advantages and the control algorithm based on DC signals are much more feasible than those based on sinusoidal signals, we presents a new state space description of DVR in terms of dq quantities that is used to derive a new control scheme, including state feedback and feed-forward path, to eliminate the source disturbance effects and the steady state error. Furthermore, the proposed state space feedback control is completed by integral control to eliminate the steady state error under variable load conditions. To compare the performance of this new control approach with that of some other control methods, some balanced and unbalanced voltage sags have been simulated on a test system in the PSCAD/EMTDC.

Grass field segmentation is the first step toward player tracking, compression and content based football image retrieval. In this paper we present two pixel-based techniques applied for grass field segmentation in football images. In the first method, the hue and a new texture feature are used for segmentation. In the second method, the hue and three wavelet features representing the spatial variation of image intensity are used to classify the image pixels into the grass and non-grass sets. Considering the feature space, in both methods, the classification process is performed using an MLP classifier. In order to evaluate the performance of the proposed methods, 800 grass and non-grass samples are selected from 40 football video clips. The test results indicated that the grass and non-grass classification accuracy were 99 and 99 percent in the fist method and 100 and 99 percent in the second method, respectively.

Most of studies carried out in the field of optimal placement of DG's are in the monopole structure. In this paper the optimal size and placement of DG's have been determined by comparing the price of electricity at various nodes supplied from grid or DG. In this pricing method in addition to the cost of losses all other cost components are considered. The price of electricity at different nodes is determined by the new location based pricing algorithm in which the required calculation is made to find out the cost of transit of electricity from sources to the specified nodes. Then the size and service area of DG's are determined. The proposed method has been applied on a real distribution network.

In this paper a circularly polarized single feed patch antenna has been optimized at the frequency of 2.45 GHz. A single stub is used in feed network to make the resonant frequency equal to circularly polarized frequency. Two different patch antennas fabricated on FR4 and RT/Duroid5870 substrates are implemented to investigate the effect of loss on antenna parameters. The measurement results confirm the integrity of simulation results.